The Mine Safety and Health Administration promulgated standards for Diesel Participate Matter (DPM) for coal and noncoal mines. The filter based methods used to enforce the new standards provide information on mass emissions, and the type of carbon. These methods do not provide real-time information on alternative exposure metrics such as particle number, surface area and volume. Reliance on these standards may underestimate the health risk resulting from exposure to Diesel exhaust when new technology is introduced. Our research will evaluate alternatives to mass based emission and time weighted average filter based standards that will enable the concentration of nuclei mode (< 30 nm in diameter) to be estimated. The response of real-time aerosol instruments is strongly influenced by the physical and chemical nature of Diesel aerosol such as particle size and composition. In a pilot study, we showed that instrument response was suppressed by the presence of a large, predominantly volatile nuclei mode, and/or the presence of volatile material on the surface of the solid carbonaceous agglomerates present in the accumulation mode (particles 30-1,000 nm). Removal of the volatile material enhanced the response, improved correlation between instruments, and provides an estimate of carbonaceous particulate matter. The long-term objective of this research is to ensure that no new health hazards are introduced underground by the use of new emission control technology. We will evaluate and recommend a suite of low-cost, real-time aerosol instruments that can be used in the laboratory, and possibly underground, to evaluate exposure/emissions and determine the physical and chemical characteristics of Diesel aerosol. The goals are: 1) evaluate the control efficiency of catalyzed emission control devices in the laboratory by measuring the particle size (number, surface area and volume), number concentration, particle volatility, mass concentration, elemental carbon (EC) and organic carbon (OC) concentration using a suite of real time instruments, 2) recommend procedures for the use of a low cost instrument package for laboratory evaluation of Diesel engines equipped with and without emission control devices, 3) develop a portable catalytic stripper for use with these instruments in underground, non-gassy mines to obtain real-time data on the physical and chemical characteristics of DPM to which miners are exposed.